qemu/target/alpha/cpu.c
Peter Maydell 28f13bccbe fpu: allow flushing of output denormals to be after rounding
Currently we handle flushing of output denormals in uncanon_normal
always before we deal with rounding.  This works for architectures
that detect tininess before rounding, but is usually not the right
place when the architecture detects tininess after rounding.  For
example, for x86 the SDM states that the MXCSR FTZ control bit causes
outputs to be flushed to zero "when it detects a floating-point
underflow condition".  This means that we mustn't flush to zero if
the input is such that after rounding it is no longer tiny.

At least one of our guest architectures does underflow detection
after rounding but flushing of denormals before rounding (MIPS MSA);
this means we need to have a config knob for this that is separate
from our existing tininess_before_rounding setting.

Add an ftz_detection flag.  For consistency with
tininess_before_rounding, we make it default to "detect ftz after
rounding"; this means that we need to explicitly set the flag to
"detect ftz before rounding" on every existing architecture that sets
flush_to_zero, so that this commit has no behaviour change.
(This means more code change here but for the long term a less
confusing API.)

For several architectures the current behaviour is either
definitely or possibly wrong; annotate those with TODO comments.
These architectures are definitely wrong (and should detect
ftz after rounding):
 * x86
 * Alpha

For these architectures the spec is unclear:
 * MIPS (for non-MSA)
 * RX
 * SH4

PA-RISC makes ftz detection IMPDEF, but we aren't setting the
"tininess before rounding" setting that we ought to.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
2025-02-11 16:22:07 +00:00

306 lines
9.4 KiB
C

/*
* QEMU Alpha CPU
*
* Copyright (c) 2007 Jocelyn Mayer
* Copyright (c) 2012 SUSE LINUX Products GmbH
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, see
* <http://www.gnu.org/licenses/lgpl-2.1.html>
*/
#include "qemu/osdep.h"
#include "qapi/error.h"
#include "qemu/qemu-print.h"
#include "cpu.h"
#include "exec/exec-all.h"
#include "exec/translation-block.h"
#include "fpu/softfloat.h"
static void alpha_cpu_set_pc(CPUState *cs, vaddr value)
{
CPUAlphaState *env = cpu_env(cs);
env->pc = value;
}
static vaddr alpha_cpu_get_pc(CPUState *cs)
{
CPUAlphaState *env = cpu_env(cs);
return env->pc;
}
static void alpha_cpu_synchronize_from_tb(CPUState *cs,
const TranslationBlock *tb)
{
/* The program counter is always up to date with CF_PCREL. */
if (!(tb_cflags(tb) & CF_PCREL)) {
CPUAlphaState *env = cpu_env(cs);
env->pc = tb->pc;
}
}
static void alpha_restore_state_to_opc(CPUState *cs,
const TranslationBlock *tb,
const uint64_t *data)
{
CPUAlphaState *env = cpu_env(cs);
if (tb_cflags(tb) & CF_PCREL) {
env->pc = (env->pc & TARGET_PAGE_MASK) | data[0];
} else {
env->pc = data[0];
}
}
static bool alpha_cpu_has_work(CPUState *cs)
{
/* Here we are checking to see if the CPU should wake up from HALT.
We will have gotten into this state only for WTINT from PALmode. */
/* ??? I'm not sure how the IPL state works with WTINT to keep a CPU
asleep even if (some) interrupts have been asserted. For now,
assume that if a CPU really wants to stay asleep, it will mask
interrupts at the chipset level, which will prevent these bits
from being set in the first place. */
return cs->interrupt_request & (CPU_INTERRUPT_HARD
| CPU_INTERRUPT_TIMER
| CPU_INTERRUPT_SMP
| CPU_INTERRUPT_MCHK);
}
static int alpha_cpu_mmu_index(CPUState *cs, bool ifetch)
{
return alpha_env_mmu_index(cpu_env(cs));
}
static void alpha_cpu_disas_set_info(CPUState *cpu, disassemble_info *info)
{
info->mach = bfd_mach_alpha_ev6;
info->print_insn = print_insn_alpha;
}
static void alpha_cpu_realizefn(DeviceState *dev, Error **errp)
{
CPUState *cs = CPU(dev);
AlphaCPUClass *acc = ALPHA_CPU_GET_CLASS(dev);
Error *local_err = NULL;
#ifndef CONFIG_USER_ONLY
/* Use pc-relative instructions in system-mode */
cs->tcg_cflags |= CF_PCREL;
#endif
cpu_exec_realizefn(cs, &local_err);
if (local_err != NULL) {
error_propagate(errp, local_err);
return;
}
qemu_init_vcpu(cs);
acc->parent_realize(dev, errp);
}
/* Models */
typedef struct AlphaCPUAlias {
const char *alias;
const char *typename;
} AlphaCPUAlias;
static const AlphaCPUAlias alpha_cpu_aliases[] = {
{ "21064", ALPHA_CPU_TYPE_NAME("ev4") },
{ "21164", ALPHA_CPU_TYPE_NAME("ev5") },
{ "21164a", ALPHA_CPU_TYPE_NAME("ev56") },
{ "21164pc", ALPHA_CPU_TYPE_NAME("pca56") },
{ "21264", ALPHA_CPU_TYPE_NAME("ev6") },
{ "21264a", ALPHA_CPU_TYPE_NAME("ev67") },
};
static ObjectClass *alpha_cpu_class_by_name(const char *cpu_model)
{
ObjectClass *oc;
char *typename;
int i;
oc = object_class_by_name(cpu_model);
if (oc != NULL && object_class_dynamic_cast(oc, TYPE_ALPHA_CPU) != NULL) {
return oc;
}
for (i = 0; i < ARRAY_SIZE(alpha_cpu_aliases); i++) {
if (strcmp(cpu_model, alpha_cpu_aliases[i].alias) == 0) {
oc = object_class_by_name(alpha_cpu_aliases[i].typename);
assert(oc != NULL && !object_class_is_abstract(oc));
return oc;
}
}
typename = g_strdup_printf(ALPHA_CPU_TYPE_NAME("%s"), cpu_model);
oc = object_class_by_name(typename);
g_free(typename);
return oc;
}
static void ev4_cpu_initfn(Object *obj)
{
cpu_env(CPU(obj))->implver = IMPLVER_2106x;
}
static void ev5_cpu_initfn(Object *obj)
{
cpu_env(CPU(obj))->implver = IMPLVER_21164;
}
static void ev56_cpu_initfn(Object *obj)
{
cpu_env(CPU(obj))->amask |= AMASK_BWX;
}
static void pca56_cpu_initfn(Object *obj)
{
cpu_env(CPU(obj))->amask |= AMASK_MVI;
}
static void ev6_cpu_initfn(Object *obj)
{
CPUAlphaState *env = cpu_env(CPU(obj));
env->implver = IMPLVER_21264;
env->amask = AMASK_BWX | AMASK_FIX | AMASK_MVI | AMASK_TRAP;
}
static void ev67_cpu_initfn(Object *obj)
{
cpu_env(CPU(obj))->amask |= AMASK_CIX | AMASK_PREFETCH;
}
static void alpha_cpu_initfn(Object *obj)
{
CPUAlphaState *env = cpu_env(CPU(obj));
/* TODO all this should be done in reset, not init */
env->lock_addr = -1;
/*
* TODO: this is incorrect. The Alpha Architecture Handbook version 4
* describes NaN propagation in section 4.7.10.4. We should prefer
* the operand in Fb (whether it is a QNaN or an SNaN), then the
* operand in Fa. That is float_2nan_prop_ba.
*/
set_float_2nan_prop_rule(float_2nan_prop_x87, &env->fp_status);
/* Default NaN: sign bit clear, msb frac bit set */
set_float_default_nan_pattern(0b01000000, &env->fp_status);
/*
* TODO: this is incorrect. The Alpha Architecture Handbook version 4
* section 4.7.7.11 says that we flush to zero for underflow cases, so
* this should be float_ftz_after_rounding to match the
* tininess_after_rounding (which is specified in section 4.7.5).
*/
set_float_ftz_detection(float_ftz_before_rounding, &env->fp_status);
#if defined(CONFIG_USER_ONLY)
env->flags = ENV_FLAG_PS_USER | ENV_FLAG_FEN;
cpu_alpha_store_fpcr(env, (uint64_t)(FPCR_INVD | FPCR_DZED | FPCR_OVFD
| FPCR_UNFD | FPCR_INED | FPCR_DNOD
| FPCR_DYN_NORMAL) << 32);
#else
env->flags = ENV_FLAG_PAL_MODE | ENV_FLAG_FEN;
#endif
}
#ifndef CONFIG_USER_ONLY
#include "hw/core/sysemu-cpu-ops.h"
static const struct SysemuCPUOps alpha_sysemu_ops = {
.get_phys_page_debug = alpha_cpu_get_phys_page_debug,
};
#endif
#include "hw/core/tcg-cpu-ops.h"
static const TCGCPUOps alpha_tcg_ops = {
.initialize = alpha_translate_init,
.translate_code = alpha_translate_code,
.synchronize_from_tb = alpha_cpu_synchronize_from_tb,
.restore_state_to_opc = alpha_restore_state_to_opc,
#ifdef CONFIG_USER_ONLY
.record_sigsegv = alpha_cpu_record_sigsegv,
.record_sigbus = alpha_cpu_record_sigbus,
#else
.tlb_fill = alpha_cpu_tlb_fill,
.cpu_exec_interrupt = alpha_cpu_exec_interrupt,
.cpu_exec_halt = alpha_cpu_has_work,
.do_interrupt = alpha_cpu_do_interrupt,
.do_transaction_failed = alpha_cpu_do_transaction_failed,
.do_unaligned_access = alpha_cpu_do_unaligned_access,
#endif /* !CONFIG_USER_ONLY */
};
static void alpha_cpu_class_init(ObjectClass *oc, void *data)
{
DeviceClass *dc = DEVICE_CLASS(oc);
CPUClass *cc = CPU_CLASS(oc);
AlphaCPUClass *acc = ALPHA_CPU_CLASS(oc);
device_class_set_parent_realize(dc, alpha_cpu_realizefn,
&acc->parent_realize);
cc->class_by_name = alpha_cpu_class_by_name;
cc->has_work = alpha_cpu_has_work;
cc->mmu_index = alpha_cpu_mmu_index;
cc->dump_state = alpha_cpu_dump_state;
cc->set_pc = alpha_cpu_set_pc;
cc->get_pc = alpha_cpu_get_pc;
cc->gdb_read_register = alpha_cpu_gdb_read_register;
cc->gdb_write_register = alpha_cpu_gdb_write_register;
#ifndef CONFIG_USER_ONLY
dc->vmsd = &vmstate_alpha_cpu;
cc->sysemu_ops = &alpha_sysemu_ops;
#endif
cc->disas_set_info = alpha_cpu_disas_set_info;
cc->tcg_ops = &alpha_tcg_ops;
cc->gdb_num_core_regs = 67;
}
#define DEFINE_ALPHA_CPU_TYPE(base_type, cpu_model, initfn) \
{ \
.parent = base_type, \
.instance_init = initfn, \
.name = ALPHA_CPU_TYPE_NAME(cpu_model), \
}
static const TypeInfo alpha_cpu_type_infos[] = {
{
.name = TYPE_ALPHA_CPU,
.parent = TYPE_CPU,
.instance_size = sizeof(AlphaCPU),
.instance_align = __alignof(AlphaCPU),
.instance_init = alpha_cpu_initfn,
.abstract = true,
.class_size = sizeof(AlphaCPUClass),
.class_init = alpha_cpu_class_init,
},
DEFINE_ALPHA_CPU_TYPE(TYPE_ALPHA_CPU, "ev4", ev4_cpu_initfn),
DEFINE_ALPHA_CPU_TYPE(TYPE_ALPHA_CPU, "ev5", ev5_cpu_initfn),
DEFINE_ALPHA_CPU_TYPE(ALPHA_CPU_TYPE_NAME("ev5"), "ev56", ev56_cpu_initfn),
DEFINE_ALPHA_CPU_TYPE(ALPHA_CPU_TYPE_NAME("ev56"), "pca56",
pca56_cpu_initfn),
DEFINE_ALPHA_CPU_TYPE(TYPE_ALPHA_CPU, "ev6", ev6_cpu_initfn),
DEFINE_ALPHA_CPU_TYPE(ALPHA_CPU_TYPE_NAME("ev6"), "ev67", ev67_cpu_initfn),
DEFINE_ALPHA_CPU_TYPE(ALPHA_CPU_TYPE_NAME("ev67"), "ev68", NULL),
};
DEFINE_TYPES(alpha_cpu_type_infos)